This invention relates to dedicated-connection switching technology used in digital communications networks and more particularly to switching technologies employing virtual channel and virtual path circuits, such as asynchronous transfer mode (ATM).
Dedicated-connection switching technologies such as asynchronous transfer mode (ATM) utilize virtual channel circuits (VCC) to transfer packets of data through and between switching nodes. Traffic management is simplified by aggregating VCC traffic onto virtual path circuits (VPC) in instances where circuits share a common route over one or more switching nodes.
It is also known that within a network, a permanent virtual path circuit (PVPC) can be utilized as a kind of virtual link onto which a plurality of VCCs can be bundled. In the event of a network failure a PVPC can be rerouted around the network failure more efficiently than a plurality of unbundled VCCs, since fewer circuits must be removed and re-established elsewhere. The shortcoming of this approach is that the exact route taken through the network by the PVPC must be centrally planned and provisioned. In the event of a network failure the central planning and provisioning authority must ensure that a new route for the PVPC is reestablished as quickly as possible. The use of a central authority for routing and rerouting the PVPC, even when automated, incurs a cost of efficiency, chiefly due to: 1) the cost of implementing and maintaining the centralized authority; 2) the cost of network management bandwidth incurred in issuing provisioning commands from the central authority to the network elements; and 3) the real time performance penalty incurred when rerouting around trouble spots, from passing information on network conditions up to the central authority, then passing routing and rerouting commands down to each network element traversed by the PVPC.
The present invention significantly reduces this efficiency cost by replacing the PVPC with a semi-permanent virtual path circuit (SPVPC), and using two different levels of connection admission control and signaling means to permit switched virtual channel circuits (SVCC) and semi-permanent virtual channel circuits (SPVCC) to utilize the SPVPC.
It is the object of the present invention to provide for the automatic provisioning and use of semi-permanent virtual path circuits for carrying virtual channels.
In accordance with a preferred embodiment of the invention each pair of nodes in the core of the network which are joined by a physical link may be configured by a network management system such that the ends of the physical link are configured with level one (or a first) connection admission control means, which permits only virtual path circuits (VPC) to utilize the physical link directly, and level one (or a first) signaling means, which attempts to remove and re-establish elsewhere the VPCs directly utilizing the physical link as soon as possible after a failure of the physical link is detected. The network management system may connect each pair of nodes at the edge of the network with a semi-permanent virtual path circuit (SPVPC). Each SPVPC thus established has level two (or a second) connection admission control means configured at each endpoint, which permits switched virtual channel circuits (SVCC) and semi-permanent virtual channel circuits (SPVCC) to utilize the SPVPC, and level two (or a second) signaling means, which in the event of a failure in the core of the network reacts more slowly than the level one signaling means, in that it attempts to remove and re-establish elsewhere the individual SVCCs and SPVCCs using the SPVPC only if the SPVPC cannot be immediately rerouted around the failure using the level one signaling and connection admission control means that exist in the core of the network.
Therefore, in accordance with a first broad aspect of the invention there is provided in a digital network having switching means to transfer packets of data between network edge nodes through a plurality of physically linked intermediate core nodes, a semi-permanent virtual path circuit (SPVPC) for routing and maintaining packet flow through the core nodes on virtual channel connections, the physical link between core nodes and the SPVPC being provisioned by a network management systems using level one and level two connection admission control and signaling respectively.
In accordance with a second aspect of the invention there is provided a method of routing and maintaining flow of data traffic between respective network edge nodes by way of intermediate core nodes in a dedicated-connection switching digital communications network, comprising: establishing a semi-permanent virtual path circuit (SPVPC) between respective edge nodes in the network for carrying virtual channel connections; identifying physical links between pairs of intermediate core nodes; provisioning the physical link to level one connection admission control and signaling whereby the physical link permits only virtual path circuit traffic and seeks alternate routing for VPCs in the event of a network failure; provisioning the SPVPC to use level two connection admission control and signaling whereby the SPVPC carries switched virtual channel circuits SVCCs and semi-permanent virtual channel circuits SPVCCs and seeks alternate routes for SVCCs and SPVCCs in the event of network failure; and configuring the level two connection admission control and signaling to respond more slowly than the level one connection admission control and signaling, whereby in the event of a network failure re-routing is set up on the SPVPC only if re-routing is not established via the physical links within a certain time.